Treating the surface of a work of art is different from treating artifacts because aesthetics is a big issue. If the artist is available, I think you should talk to him or her first about preferences related to the appearance of the metal surface.
Taking off rust with wire brushes can leave scratches which, in turn, will promote more rusting, and, inevitably, the piece will rust again, even if you slow down the process. Typically, when bronze outdoor sculptures are treated, after the cleaning, a resinous coating is applied first, with wax on top. The wax can be removed and re-applied without removing the resinous coating. I don’t know if this approach is transferable to steel, but I recommend getting more information from conservators who treat this kind of sculpture before you do anything.